Can't change background of window

Question

I develop a win32 app and create a color chooser using this example. I update if statement like this to change the background of my app when user click to "Ok" in color dialog box, but nothing change. Where is my mistake?

if (ChooseColor(&cc) == TRUE) {
    HBRUSH hbrush = CreateSolidBrush(cc.rgbResult);
    rgbCurrent = cc.rgbResult;
    SetClassLongPtr(hWnd, GCLP_HBRBACKGROUND, (LONG)hbrush);
}

You need to use a static brush. Creating a new one each time means resource leak. — DimChtz, Mar 26 '16 at 15:12
You need WM_ERASEBKGND, see the accepted anwser in the SO link you posted. — Joel, Mar 26 '16 at 16:30
Don't cast `hbrush` to `LONG`, the whole point of `SetClassLongPtr` is that the parameter is a `LONG_PTR`. — Jonathan Potter, Mar 26 '16 at 19:46
Anyway, I don't understand, I add `case WM_ERASEBKGND: wc.hbrBackground = (HBRUSH)GetSysColorBrush(COLOR_3DFACE);` but nothing change. — rel1x, Mar 27 '16 at 20:20
I tried to fix it all day today. I don't follow how to do it. — rel1x, Mar 27 '16 at 20:23

Chanhee Jo · Answer 1 · 2016-03-28T04:29:27.837

2

The following code would work.

First, SetClassLongPtr() returns the previous value, which is, in this case, the HBRUSH previously set to the window class(hWnd). You should delete the object to avoid memory leak.

After that, calling InvalidateRect() brings the color change into effect. Because the newly created brush will be used when the window needs to be repainted.

InvalidateRect() sends WM_ERASEBKGND to the window.

if (ChooseColor(&cc) == TRUE) {
    HBRUSH hbrush = CreateSolidBrush(cc.rgbResult);
    HBRUSH hOldBrush = (HBRUSH)SetClassLongPtr(hWnd, GCLP_HBRBACKGROUND, (LONG_PTR)hbrush);

    DeleteObject(hOldBrush);
    InvalidateRect(hWnd, NULL, 1);
}

edited Mar 28 '16 at 04:29

answered Mar 28 '16 at 03:25

Chanhee Jo

199
6

1

Note that this changes the background color for all Windows of the class, not just the one represented by `hWnd`. You should custom erase the window with `WM_ERASEBKGND` so that only the one window changes its background color. – Raymond Chen Mar 28 '16 at 03:36

Can't change background of window

1 Answers1